1. Field of the Invention
The present invention relates to an optical device having a lightwave circuit element.
2. Description of the Background Art
An example of an optical device is a directional coupler that has first and second optical waveguides disposed in mutual proximity in a fixed range and lightwaves guided respectively through each of the waveguides are coupled therebetween.
The optical device disclosed in Japanese Patent Application Publication No. 2003-215647 is provided with a hollow area filled with resin between the first and second optical waveguides in the optical coupling area of the directional coupler which is formed on a substrate. The temperature of the resin is adjusted via an overcladding layer or the substrate. By modifying the temperature of the resin, the refractive index of the resin is changed, and the optical characteristics (optical branching ratio, for example) of the directional coupler are thereby changed.
The optical device disclosed in Japanese Patent Application Publication No. 2000-066044 (corresponding European patent application publication No. 981 064) uses a polymer material in the core area or cladding area. The refractive index of the polymer material is changed and the state (phase, for example) of the light guided through the core area is modified by changing the temperature of the polymer material.
The optical device disclosed in Japanese Patent Application Publication No. 2000-111964 (corresponding U.S. Pat. No. 6,310,999) uses a polymer material in the periphery of the first and second waveguides in the optical coupling area of the directional coupler which is formed on a substrate. The refractive index of the polymer material is changed by modifying the temperature of the polymer material and thereby the optical branching ratio of the directional coupler is changed.
The power required to vary the temperature of the resins is considerable with the optical devices disclosed in the prior art.